The present invention relates to a photochromic plastic object, constructed from a transparent polymer plastic material, at least one essentially mesoporous inorganic host structure, which has one or more organic photochromic dye molecules (i.e., coloring agents) intercalated, being introduced therein or attached thereto to form a photochromic nanocomposite material. In contrast to the approaches available in the prior art, according to the present invention, photochromic organic dyes are not added in molecular form to the monomer mixture/pre-polymers of the plastic glass, but rather photochromic nanocomposite particles and/or photochromic nanocomposite structures are used to generate the coloration.
Photochromic plastic objects in general and phototropic spectacle lenses made of plastic especially may be produced using photochromic organic dyes. The dyes for phototropic spectacle lenses must fulfill various requirements: (i) high extinction coefficients, (ii) light resistance/high service life, (iii) controllable color curve upon darkening and lightening, (iv) good kinetic properties in darkening and lightening at different temperatures, and (v) compatibility with the polymer substrate. These requirements are fulfilled in particular by compounds made of the substance class of pyrans, in particular naphthopyrans and larger ring systems derived therefrom. Spirooxazine and spiropyran dyes, which were the state-of-the-art until the second half of the 90s, are also suitable for use in ophthalmic lenses.
The dyeing of transparent plastic for use as spectacle lenses is performed industrially in various ways: (i) by compound dyeing, dye being added to the monomer mixture before the polymerization, (ii) by application of a photochromic thin-film, the substrate being provided with a film having a functional layer producible according to method (i) using spin coating, dip coating, etc., or gluing, or (iii) by surface dyeing, the dyeing being performed by thermodiffusion of the photochromic dyes into the plastic object.
The dye molecules are thus influenced chemically and physically in a new environment—a matrix—and must be adapted thereto. Different plastics and polymer compositions are used in the production of spectacle lenses, as a result of the requirements for the product and its intended use. The cured polymers differ in index of refraction, hardness, impact resistance, weight, etc.
A change of the polymer matrix may have negative effects on the photochromic behavior of the organic dye and thus result in significant efforts in research and development or even prevent the commercial use of the dye class. Therefore, it is noted in U.S. Pat. No. 6,373,615 (=DE 198 52 680) that a comparative study of dyes may only be performed in identical matrices.
The dye and surrounding matrix are parts of the photochromic system and thus cannot be observed independently of one another. The photochromic properties are controlled on one hand by the selection of the dye class and substitution of its basic framework and on the other hand by the surrounding matrix. If it is possible to make the dyes independent of the matrix effects of the plastic material of the ophthalmic lenses, the above restrictions no longer apply. An approach for removing these existing restrictions is described in EP 1 099 743 A1. A “protective envelope” for the isomeric center of the ring-opening dye is described therein, which is adapted in its molecular dimensions.